At the time the LLM generated the compiler, just syntax. The semantics it generated were the subset of C that the C version of the compiler already used.

You could set the goalposts such that it wasn't novel enough to count, but for a short time I had code running in a language that nobody had ever known. Getting it from that point to a language that's ergonomic to use, teaches something about computing, or both is a longer journey, and certainly not one an LLM could take on its own.

An LLM won't come up with an interesting CRUD app on its own either. Parts of that process are pretty mechanical, but we had skeletons and templates before we had LLMs.